perf pmu: Make the loading of formats lazy

The sysfs format files are loaded eagerly in a PMU. Add a flag so that
we create the format but only load the contents when necessary.

Reduce the size of the value in struct perf_pmu_format and avoid holes
so there is no additional space requirement.

For "perf stat -e cycles true" this reduces the number of openat calls
from 648 to 573 (about 12%). The benchmark pmu scan speed is improved
by roughly 5%.

Before:

  $ perf bench internals pmu-scan
  Computing performance of sysfs PMU event scan for 100 times
    Average core PMU scanning took: 1061.100 usec (+- 9.965 usec)
    Average PMU scanning took: 4725.300 usec (+- 260.599 usec)

After:

  $ perf bench internals pmu-scan
  Computing performance of sysfs PMU event scan for 100 times
    Average core PMU scanning took: 989.170 usec (+- 6.873 usec)
    Average PMU scanning took: 4520.960 usec (+- 251.272 usec)

Committer testing:

On a AMD Ryzen 5950x:

Before:

  $ perf bench internals pmu-scan -i1000
  # Running 'internals/pmu-scan' benchmark:
  Computing performance of sysfs PMU event scan for 1000 times
    Average core PMU scanning took: 563.466 usec (+- 1.008 usec)
    Average PMU scanning took: 1619.174 usec (+- 23.627 usec)
  $ perf stat -r5 perf bench internals pmu-scan -i1000
  # Running 'internals/pmu-scan' benchmark:
  Computing performance of sysfs PMU event scan for 1000 times
    Average core PMU scanning took: 583.401 usec (+- 2.098 usec)
    Average PMU scanning took: 1677.352 usec (+- 24.636 usec)
  # Running 'internals/pmu-scan' benchmark:
  Computing performance of sysfs PMU event scan for 1000 times
    Average core PMU scanning took: 553.254 usec (+- 0.825 usec)
    Average PMU scanning took: 1635.655 usec (+- 24.312 usec)
  # Running 'internals/pmu-scan' benchmark:
  Computing performance of sysfs PMU event scan for 1000 times
    Average core PMU scanning took: 557.733 usec (+- 0.980 usec)
    Average PMU scanning took: 1600.659 usec (+- 23.344 usec)
  # Running 'internals/pmu-scan' benchmark:
  Computing performance of sysfs PMU event scan for 1000 times
    Average core PMU scanning took: 554.906 usec (+- 0.774 usec)
    Average PMU scanning took: 1595.338 usec (+- 23.288 usec)
  # Running 'internals/pmu-scan' benchmark:
  Computing performance of sysfs PMU event scan for 1000 times
    Average core PMU scanning took: 551.798 usec (+- 0.967 usec)
    Average PMU scanning took: 1623.213 usec (+- 23.998 usec)

   Performance counter stats for 'perf bench internals pmu-scan -i1000' (5 runs):

             3276.82 msec task-clock:u                     #    0.990 CPUs utilized               ( +-  0.82% )
                   0      context-switches:u               #    0.000 /sec
                   0      cpu-migrations:u                 #    0.000 /sec
                1008      page-faults:u                    #  307.615 /sec                        ( +-  0.04% )
         12049614778      cycles:u                         #    3.677 GHz                         ( +-  0.07% )  (83.34%)
           117507478      stalled-cycles-frontend:u        #    0.98% frontend cycles idle        ( +-  0.33% )  (83.32%)
            27106761      stalled-cycles-backend:u         #    0.22% backend cycles idle         ( +-  9.55% )  (83.36%)
         33294953848      instructions:u                   #    2.76  insn per cycle
                                                           #    0.00  stalled cycles per insn     ( +-  0.03% )  (83.31%)
          6849825049      branches:u                       #    2.090 G/sec                       ( +-  0.03% )  (83.37%)
            71533903      branch-misses:u                  #    1.04% of all branches             ( +-  0.20% )  (83.30%)

              3.3088 +- 0.0302 seconds time elapsed  ( +-  0.91% )

  $

After:

  $ perf stat -r5 perf bench internals pmu-scan -i1000
  # Running 'internals/pmu-scan' benchmark:
  Computing performance of sysfs PMU event scan for 1000 times
    Average core PMU scanning took: 550.702 usec (+- 0.958 usec)
    Average PMU scanning took: 1566.577 usec (+- 22.747 usec)
  # Running 'internals/pmu-scan' benchmark:
  Computing performance of sysfs PMU event scan for 1000 times
    Average core PMU scanning took: 548.315 usec (+- 0.555 usec)
    Average PMU scanning took: 1565.499 usec (+- 22.760 usec)
  # Running 'internals/pmu-scan' benchmark:
  Computing performance of sysfs PMU event scan for 1000 times
    Average core PMU scanning took: 548.073 usec (+- 0.555 usec)
    Average PMU scanning took: 1586.097 usec (+- 23.299 usec)
  # Running 'internals/pmu-scan' benchmark:
  Computing performance of sysfs PMU event scan for 1000 times
    Average core PMU scanning took: 561.184 usec (+- 2.709 usec)
    Average PMU scanning took: 1567.153 usec (+- 22.548 usec)
  # Running 'internals/pmu-scan' benchmark:
  Computing performance of sysfs PMU event scan for 1000 times
    Average core PMU scanning took: 546.987 usec (+- 0.553 usec)
    Average PMU scanning took: 1562.814 usec (+- 22.729 usec)

   Performance counter stats for 'perf bench internals pmu-scan -i1000' (5 runs):

             3170.86 msec task-clock:u                     #    0.992 CPUs utilized               ( +-  0.22% )
                   0      context-switches:u               #    0.000 /sec
                   0      cpu-migrations:u                 #    0.000 /sec
                1010      page-faults:u                    #  318.526 /sec                        ( +-  0.04% )
         11890047674      cycles:u                         #    3.750 GHz                         ( +-  0.14% )  (83.27%)
           119090499      stalled-cycles-frontend:u        #    1.00% frontend cycles idle        ( +-  0.46% )  (83.40%)
            32502449      stalled-cycles-backend:u         #    0.27% backend cycles idle         ( +-  8.32% )  (83.30%)
         33119141261      instructions:u                   #    2.79  insn per cycle
                                                    #    0.00  stalled cycles per insn     ( +-  0.01% )  (83.37%)
          6812816561      branches:u                       #    2.149 G/sec                       ( +-  0.01% )  (83.29%)
            70157855      branch-misses:u                  #    1.03% of all branches             ( +-  0.28% )  (83.38%)

             3.19710 +- 0.00826 seconds time elapsed  ( +-  0.26% )

  $
Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Gaosheng Cui <cuigaosheng1@huawei.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jing Zhang <renyu.zj@linux.alibaba.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230824041330.266337-2-irogers@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/pmu.c

@@ -171,7 +171,7 @@ static int test__pmu(struct test_suite *test __maybe_unused, int subtest __maybe
 	}
 
 	pmu->name = strdup("perf-pmu-test");
-	ret = perf_pmu__format_parse(pmu, fd);
+	ret = perf_pmu__format_parse(pmu, fd, /*eager_load=*/true);
 	if (ret)
 		goto out;
 

tools/perf/util/pmu.c

@@ -40,6 +40,10 @@ struct perf_pmu perf_pmu__fake;
  * value=PERF_PMU_FORMAT_VALUE_CONFIG and bits 0 to 7 will be set.
  */
 struct perf_pmu_format {
+	/** @list: Element on list within struct perf_pmu. */
+	struct list_head list;
+	/** @bits: Which config bits are set by this format value. */
+	DECLARE_BITMAP(bits, PERF_PMU_FORMAT_BITS);
 	/** @name: The modifier/file name. */
 	char *name;
 	/**
@@ -47,18 +51,79 @@ struct perf_pmu_format {
 	 * are from PERF_PMU_FORMAT_VALUE_CONFIG to
 	 * PERF_PMU_FORMAT_VALUE_CONFIG_END.
 	 */
-	int value;
-	/** @bits: Which config bits are set by this format value. */
-	DECLARE_BITMAP(bits, PERF_PMU_FORMAT_BITS);
-	/** @list: Element on list within struct perf_pmu. */
-	struct list_head list;
+	u16 value;
+	/** @loaded: Has the contents been loaded/parsed. */
+	bool loaded;
 };
 
+static struct perf_pmu_format *perf_pmu__new_format(struct list_head *list, char *name)
+{
+	struct perf_pmu_format *format;
+
+	format = zalloc(sizeof(*format));
+	if (!format)
+		return NULL;
+
+	format->name = strdup(name);
+	if (!format->name) {
+		free(format);
+		return NULL;
+	}
+	list_add_tail(&format->list, list);
+	return format;
+}
+
+/* Called at the end of parsing a format. */
+void perf_pmu_format__set_value(void *vformat, int config, unsigned long *bits)
+{
+	struct perf_pmu_format *format = vformat;
+
+	format->value = config;
+	memcpy(format->bits, bits, sizeof(format->bits));
+}
+
+static void __perf_pmu_format__load(struct perf_pmu_format *format, FILE *file)
+{
+	void *scanner;
+	int ret;
+
+	ret = perf_pmu_lex_init(&scanner);
+	if (ret)
+		return;
+
+	perf_pmu_set_in(file, scanner);
+	ret = perf_pmu_parse(format, scanner);
+	perf_pmu_lex_destroy(scanner);
+	format->loaded = true;
+}
+
+static void perf_pmu_format__load(struct perf_pmu *pmu, struct perf_pmu_format *format)
+{
+	char path[PATH_MAX];
+	FILE *file = NULL;
+
+	if (format->loaded)
+		return;
+
+	if (!perf_pmu__pathname_scnprintf(path, sizeof(path), pmu->name, "format"))
+		return;
+
+	assert(strlen(path) + strlen(format->name) + 2 < sizeof(path));
+	strcat(path, "/");
+	strcat(path, format->name);
+
+	file = fopen(path, "r");
+	if (!file)
+		return;
+	__perf_pmu_format__load(format, file);
+	fclose(file);
+}
+
 /*
  * Parse & process all the sysfs attributes located under
  * the directory specified in 'dir' parameter.
  */
-int perf_pmu__format_parse(struct perf_pmu *pmu, int dirfd)
+int perf_pmu__format_parse(struct perf_pmu *pmu, int dirfd, bool eager_load)
 {
 	struct dirent *evt_ent;
 	DIR *format_dir;
@@ -68,37 +133,35 @@ int perf_pmu__format_parse(struct perf_pmu *pmu, int dirfd)
 	if (!format_dir)
 		return -EINVAL;
 
-	while (!ret && (evt_ent = readdir(format_dir))) {
+	while ((evt_ent = readdir(format_dir)) != NULL) {
+		struct perf_pmu_format *format;
 		char *name = evt_ent->d_name;
-		int fd;
-		void *scanner;
-		FILE *file;
 
 		if (!strcmp(name, ".") || !strcmp(name, ".."))
 			continue;
 
-
-		ret = -EINVAL;
-		fd = openat(dirfd, name, O_RDONLY);
-		if (fd < 0)
-			break;
-
-		file = fdopen(fd, "r");
-		if (!file) {
-			close(fd);
+		format = perf_pmu__new_format(&pmu->format, name);
+		if (!format) {
+			ret = -ENOMEM;
 			break;
 		}
 
-		ret = perf_pmu_lex_init(&scanner);
-		if (ret) {
+		if (eager_load) {
+			FILE *file;
+			int fd = openat(dirfd, name, O_RDONLY);
+
+			if (fd < 0) {
+				ret = -errno;
+				break;
+			}
+			file = fdopen(fd, "r");
+			if (!file) {
+				close(fd);
+				break;
+			}
+			__perf_pmu_format__load(format, file);
 			fclose(file);
-			break;
 		}
-
-		perf_pmu_set_in(file, scanner);
-		ret = perf_pmu_parse(&pmu->format, name, scanner);
-		perf_pmu_lex_destroy(scanner);
-		fclose(file);
 	}
 
 	closedir(format_dir);
@@ -119,7 +182,7 @@ static int pmu_format(struct perf_pmu *pmu, int dirfd, const char *name)
 		return 0;
 
 	/* it'll close the fd */
-	if (perf_pmu__format_parse(pmu, fd))
+	if (perf_pmu__format_parse(pmu, fd, /*eager_load=*/false))
 		return -1;
 
 	return 0;
@@ -962,13 +1025,15 @@ void perf_pmu__warn_invalid_formats(struct perf_pmu *pmu)
 	if (pmu == &perf_pmu__fake)
 		return;
 
-	list_for_each_entry(format, &pmu->format, list)
+	list_for_each_entry(format, &pmu->format, list) {
+		perf_pmu_format__load(pmu, format);
 		if (format->value >= PERF_PMU_FORMAT_VALUE_CONFIG_END) {
 			pr_warning("WARNING: '%s' format '%s' requires 'perf_event_attr::config%d'"
 				   "which is not supported by this version of perf!\n",
 				   pmu->name, format->name, format->value);
 			return;
 		}
+	}
 }
 
 bool evsel__is_aux_event(const struct evsel *evsel)
@@ -1041,6 +1106,7 @@ int perf_pmu__format_type(struct perf_pmu *pmu, const char *name)
 	if (!format)
 		return -1;
 
+	perf_pmu_format__load(pmu, format);
 	return format->value;
 }
 
@@ -1177,7 +1243,7 @@ static int pmu_config_term(struct perf_pmu *pmu,
 		free(pmu_term);
 		return -EINVAL;
 	}
-
+	perf_pmu_format__load(pmu, format);
 	switch (format->value) {
 	case PERF_PMU_FORMAT_VALUE_CONFIG:
 		vp = &attr->config;
@@ -1403,24 +1469,6 @@ struct perf_pmu_alias *perf_pmu__find_alias(struct perf_pmu *pmu, const char *ev
 
 	return NULL;
 }
-
-int perf_pmu__new_format(struct list_head *list, char *name,
-			 int config, unsigned long *bits)
-{
-	struct perf_pmu_format *format;
-
-	format = zalloc(sizeof(*format));
-	if (!format)
-		return -ENOMEM;
-
-	format->name = strdup(name);
-	format->value = config;
-	memcpy(format->bits, bits, sizeof(format->bits));
-
-	list_add_tail(&format->list, list);
-	return 0;
-}
-
 static void perf_pmu__del_formats(struct list_head *formats)
 {
 	struct perf_pmu_format *fmt, *tmp;

tools/perf/util/pmu.h

@@ -227,9 +227,8 @@ int perf_pmu__check_alias(struct perf_pmu *pmu, struct list_head *head_terms,
 			  struct perf_pmu_info *info);
 struct perf_pmu_alias *perf_pmu__find_alias(struct perf_pmu *pmu, const char *event);
 
-int perf_pmu__new_format(struct list_head *list, char *name,
-			 int config, unsigned long *bits);
-int perf_pmu__format_parse(struct perf_pmu *pmu, int dirfd);
+int perf_pmu__format_parse(struct perf_pmu *pmu, int dirfd, bool eager_load);
+void perf_pmu_format__set_value(void *format, int config, unsigned long *bits);
 bool perf_pmu__has_format(const struct perf_pmu *pmu, const char *name);
 
 bool is_pmu_core(const char *name);

tools/perf/util/pmu.y

 %define api.pure full
-%parse-param {struct list_head *format}
-%parse-param {char *name}
+%parse-param {void *format}
 %parse-param {void *scanner}
 %lex-param {void* scanner}
 
@@ -21,7 +20,7 @@ do { \
                 YYABORT; \
 } while (0)
 
-static void perf_pmu_error(struct list_head *list, char *name, void *scanner, char const *msg);
+static void perf_pmu_error(void *format, void *scanner, const char *msg);
 
 static void perf_pmu__set_format(unsigned long *bits, long from, long to)
 {
@@ -59,16 +58,12 @@ format_term
 format_term:
 PP_CONFIG ':' bits
 {
-	ABORT_ON(perf_pmu__new_format(format, name,
-				      PERF_PMU_FORMAT_VALUE_CONFIG,
-				      $3));
+	perf_pmu_format__set_value(format, PERF_PMU_FORMAT_VALUE_CONFIG, $3);
 }
 |
 PP_CONFIG PP_VALUE ':' bits
 {
-	ABORT_ON(perf_pmu__new_format(format, name,
-				      $2,
-				      $4));
+	perf_pmu_format__set_value(format, $2, $4);
 }
 
 bits:
@@ -95,9 +90,8 @@ PP_VALUE
 
 %%
 
-static void perf_pmu_error(struct list_head *list __maybe_unused,
-		    char *name __maybe_unused,
-		    void *scanner __maybe_unused,
-		    char const *msg __maybe_unused)
+static void perf_pmu_error(void *format __maybe_unused,
+			   void *scanner __maybe_unused,
+			   const char *msg __maybe_unused)
 {
 }